The present disclosure relates to an engine cooling apparatus.
An engine cooling apparatus described in Japanese Laid-Open Patent Publication No. 2013-234605 is known. The engine cooling apparatus of this document includes a coolant circuit in which coolant circulates through a water jacket, a water pump that discharges the coolant into the water jacket, and a coolant stopping mechanism that blocks return flow of coolant to the water pump after the coolant has passed through the water jacket. By blocking the return flow of coolant during engine warm-up, the coolant stopping mechanism performs coolant stopping control to stop coolant circulation in the coolant circuit. This restrains the coolant flowing in the water jacket from taking away heat from the engine, thus promoting the engine warm-up.
By arranging the aforementioned coolant stopping mechanism in a cooling apparatus for a V engine having water jackets each provided in one of the banks to perform the coolant stopping control during engine warm-up, the engine warm-up can be promoted. Some cooling apparatuses for V engines include a mechanical water pump having two discharge holes, each of which independently discharges coolant into the water jacket of one of the two banks. In a cooling apparatus for a V engine employing this water pump, a sufficient warm-up promoting effect may not be obtained through the coolant stopping control.
FIG. 7 shows an example of a coolant circuit of an engine cooling apparatus employed in a V engine having water jackets 50F, 50S, each of which is arranged in one of the banks. The engine cooling apparatus includes a mechanical water pump 52 having two discharge holes 51F, 51S and a coolant stopping mechanism 53, which stops coolant circulation.
As shown in FIG. 7, in the engine cooling apparatus, the two discharge holes 51F, 51S of the water pump 52 are each joined to the corresponding one of the water jackets 50F, 50S through one of joint passage 54F, 54S. A merging portion 55, in which the coolant merges after passing through each of the water jackets 50F, 50S, is arranged downstream of the water jackets 50F, 50S. In the engine cooling apparatus, a coolant circuit is configured such that, after passing through the water jackets 50F, 50S and merging in the merging portion 55, the coolant returns to a suction hole 57 of the water pump 52 through a radiator 56.
A coolant stopping mechanism 53 is arranged at a position between the merging portion 55 and the radiator 56 in the coolant circuit. By blocking coolant flow from the merging portion 55 to the radiator 56 by means of the coolant stopping mechanism 53, coolant stopping control is performed to stop coolant circulation in the coolant circuit.
The mechanical water pump 52, which is driven by rotation of the crankshaft, or the output shaft of the engine, is driven continuously when the coolant circulation in the coolant circuit is stopped. At the time point at which the coolant stopping control is started, a certain amount of coolant remains in the section from the coolant stopping mechanism 53 to the suction hole 57 in the coolant circuit. Therefore, after the coolant stopping mechanism is started, the water pump 52 continues to draw in coolant through the suction hole 57 and discharges the drawn coolant through the discharge holes 51F, 51S for a certain period of time.
In some cases, depending on the layout of auxiliary devices of the engine, the discharge holes 51F, 51S and the joint passages 54F, 54S may have different sizes and/or shapes between the banks. In such cases, the coolant discharge capacity of the water pump 52 may differ between the discharge hole 51F and the discharge hole 518.
In the engine cooling apparatus shown in FIG. 7, the downstream sides of the water jackets 50F, SOS of the two banks are coupled to each other through the merging portion 55. This forms a path that connects the two discharge holes 51F, 51S to each other through the water jackets 50F, 50S during the coolant stopping control. If there is a difference in discharge capacity between the discharge holes 51F and 51S, the coolant discharged from the one of the discharge holes of the greater discharge capacity pushes back the coolant discharged from the other discharge hole of the smaller discharge capacity. This causes circulation of the coolant through the water jackets 50F, 50S. For example, if the discharge capacity from the discharge hole 51F is greater, a coolant circulation occurs such that, as represented by the arrow of the broken line in FIG. 7, the coolant is discharged from the discharge hole 51F, passes through the joint passage 54F, the water jacket 50F, the merging portion 55, the water jacket 50S, and the joint passage 54S, and returns to the discharge hole 518. In contrast, if the discharge capacity from the discharge hole 51S is greater, coolant circulation occurs in the reverse order to the coolant circulation represented by the arrow of the broken line. Once such circulation occurs, the coolant is continuously drawn from the discharge hole corresponding to the smaller discharge capacity even when the coolant cannot be drawn in through the suction hole 57. As a result, such coolant circulation may continue during the coolant stopping control.
Also, even without coolant circulation in the above-described manners, the water pump 52 may draw in coolant from one of the discharge holes 51F, 51S, through which the coolant can be drawn comparatively easily, if the water pump 52 cannot draw in the coolant through the suction hole 57. The water pump 52 then discharges the drawn coolant through the other one of the discharge holes, thus causing coolant circulation in the same manner as the above-described case.
The flow rate of the coolant circulation during the coolant stopping control is low compared to the flow rate of the normal coolant circulation in the coolant circuit. However, this causes the coolant to flow into the water jackets 50F, 50S, even by a small amount, when such coolant flow should not be occurring in the water jackets 50F, 50S. The effect of promoting engine warm-up by the coolant stopping control is thus reduced. Further, even during the coolant stopping control, a slight amount of coolant enters and exits through the suction hole 57. If coolant circulates in the above-described manner and cold coolant enters through the suction hole 57 from the exterior of the engine 10, the cold coolant is mixed with the coolant circulating through the water jackets 50F, 50S. This delays increase of the coolant temperature in each of the water jackets 50F, 50S.
Even slightly different sizes and shapes of the discharge holes 51F, 51S and the joint passages 54F, 54S may cause coolant circulation in the above-described manner. Once a flow of circulating coolant is formed, circulation of the coolant is further promoted. Even an initially slight flow rate of circulating coolant thus may become a measurable flow rate eventually. Therefore, not only when the sizes and the shapes of the discharge holes 51F, 51S and the joint passages 54F, 54S are differentiated intentionally, but also the sizes and shapes are designed to be the same, a slight difference in the sizes and shapes due to machining errors may cause coolant circulation in the above-described manners.